Project Summary Global pandemic influenza vaccine production capacity is insufficient to meet the expected demand in the event of a highly lethal influenza pandemic. Current H5N1 vaccines require high antigen doses (e.g. 90 ?g) or are combined with squalene-based oil-in-water emulsion adjuvants for enhanced and broadened immunogenicity as well as antigen dose sparing. Squalene is a naturally occurring oligoisoprene (i.e. a very low molecular weight polymer of isoprene) derived from shark liver, a source with sustainability concerns. Moreover, the biological mechanisms of action of squalene are still not well understood and no systematic comparison of the adjuvant activity of squalene emulsions compared to emulsions based on analog oligoisoprenes has been reported in the literature. This proposal defines a program to develop the sustainable production of various oligoisoprene analogues of squalene using bioengineered organisms and synthetic polymer chemistry. Selected structures will then be formulated in oil-in-water emulsions and evaluated for physicochemical stability. Importantly, we propose to identify structure-activity relationships (SAR) by employing squalene and oligoisoprene analogues in in vitro human and in vivo mouse models in combination with an H5N1 influenza antigen. Moreover, the ability to further enhance adjuvant activity by chemical modification to improve physicochemical properties of selected oligoisoprene structures will be evaluated. The technology generated could be applicable to many other vaccines that have need of emulsion-based adjuvants for antigen dose sparing or enhanced immune responses.